The present invention relates to technology for controlling display and, specifically, to technology that can be particularly effectively adapted to controlling the drive of liquid crystal, such as technology that can be effectively utilized in a display control circuit in a dot-matrix liquid crystal panel for displaying characters or in a liquid crystal panel having a function of displaying pictures, marks, icons, characters (figures), etc. independently of the dot-matrix character display.
A liquid crystal display device, in general, comprises a liquid crystal display panel, a liquid crystal display controller formed as an integrated circuit on a semiconductor substrate for driving the liquid crystal display panel, and a microprocessor (MPU) or a microcontroller including a microprocessing unit (CPU) for controlling the writing of display data or the display operation of the liquid crystal display controller.
A liquid crystal display controller including a character generator for forming a display pattern of dot-matrix type is constituted by a display data memory for storing character codes (hereinafter referred to as a random access memory for display data or a display data RAM), a character generator memory for storing character patterns such as character fonts (hereinafter referred to as a read-only memory for a character generator or a character generator ROM), an address counter for reading display data from the display data RAM in accordance with the drive position of the liquid crystal display panel, a liquid crystal drive circuit for driving the liquid crystal by generating drive signals for common electrodes and for segment electrodes of a liquid crystal display panel, and a timing generation circuit for generating clock signals that give display timings.
The microprocessor writes, onto the display data RAM, character codes corresponding to characters to be displayed on the liquid crystal display panel. An address counter successively reads out character codes from the display data RAM in accordance with the drive position of the liquid crystal display panel, and successively reads out character patterns by making access to the character generator ROM by using character codes that are read out as part of the addresses. The character patterns that are read out are successively sent, as liquid crystal turn-on/off data, to a segment shift register in the liquid crystal drive circuit. When the data of one line are accumulated, the whole segment driver circuits output the drive voltages of the turn-on/turn-off level simultaneously thereby to drive the liquid crystal display panel.
Each character is constituted by a plurality of lines in a vertical direction and, hence, the above-mentioned control operation is repeated by the number of lines of the character for every display row (8 lines when the character comprises 5 (horizontal).times.8 (vertical) dots). The turn-on/turn-off control operation for the display is executed in a time-division manner for each of the lines. Therefore, a selection signal of one line generated from the timing control circuit is sent to a common shift register. As the shift register shifts for each line, a common driver successively outputs a drive voltage of the selection level of the line.